Processes for the production of methanol by reacting a gaseous mixture comprising hydrogen and carbon monoxide in the presence of a catalyst composition in a fluidized bed have been disclosed in the prior art. Also it is known in the art to use a slurry of a heterogeneous catalyst in an inert liquid for this reaction.
A lecture reporting work by Y. Saito, M. Kuwa and O. Hashimoto during the 1987 Annual Meeting of the American Institute of Chemical Engineers, New York, Nov. 15-20, 1978, entitled "Development of a fluidized-bed methanol synthesis process" discloses a process using a reactor with the catalyst in a fluidized bed, cooled by means of a cooling jacket covering the surrounding wall of the bed. The temperature was adjusted by the temperature of the coolant (water being converted into high pressure steam). This process requires high space velocities and causes a considerable drop in pressure over the reactor, the conversion per pass was about 16%. Unconverted carbon monoxide and hydrogen were recompressed and recycled through the reactor.
A lecture reporting work by M. F. M. Post; S. T. Sie and J. M. Oelderik during the Chemeca '88 (Australia's Bicentennial International Conference for the process industries), Sydney Aug. 28-31, 1988, entitled "Synthesis of Methanol in A Fluidized Bed of Catalyst" discloses fluidized bed methanol synthesis at bench scale with conversions up to 60% at 8.1 MPa and 250.degree. C. (523.degree. K.) and good catalyst stability. For commercial operations the conversions were too low however.
Also there is Chemical Week, 36 Apr. 16, 1980) disclosing a process known as Chem Systems' three-phase process in which an inert liquid was used to fluidize the catalyst and to remove the heat of reaction. Good conversions per pass are claimed, however, the inert liquid caused transport problems and affected the reaction rate. The process also required separation of methanol from the entrained inert liquid.
Cheap methanol in very large quantities is valuable product as a fuel and a starting material for further chemical processing. Therefore there is a need for an economically attractive industrial bulk manufacturing process, using cheap starting materials and operating under attractive economical, environmental and safe conditions, i.e. using rather simple equipment and resulting in a significant reduction of the methanol cost price. Therefore, considerable research and development efforts have been made for a further improved methanol manufacturing process.
The formation of methanol from hydrogen and carbon monoxide is a strongly exothermic equilibrium reaction so that relatively high operating pressures and temperatures are required for reasonable reaction rates, but under such reaction conditions the attainable conversion is strongly limited by the thermodynamic equilibrium. Finding a satisfactory compromise as to the reaction conditions between reaction rate and conversion percentage is therefore difficult. Effective control of the reaction temperature across the catalyst bed proved to be especially important.
In industrially applied processes, in which the catalyst is present in the form of a fixed bed of particles, high gas velocities are applied to promote effective removal of reaction heat and to allow good control of the reaction temperature. Due to these high velocities and the thermodynamic limitations low conversions per pass (i.e. less than 30%) are obtained. To achieve acceptable yields of methanol from synthesis gas it is customary to recompress unconverted synthesis gas and recycle it to the reactor inlet. This requires recycle compressors of large capacities, which are costly and have high power consumptions.
An object of the present invention is the development of an industrial process for methanol manufacture with satisfactory conversion percentages in relatively simple equipment.